1. Field of the Invention
The invention relates to telecommunications, and in particular, to mitigating differential delay in diverse backhaul environments.
2. Description of the Prior Art
Cellular communication networks often times include wireless devices that transmit communications to base station transceivers. The base station transceivers transfer the communications over a cellular backhaul to a mobile switching center (MSC). The MSC then routes the communications to their appropriate destination. T-1 lines are typically used for the backhaul. Packet based transports are also frequently used for the backhaul. For example, simulated T-1 over Ethernet is commonly used for the backhaul. In yet another example, many carriers are beginning to use WiMAX technologies for cellular backhaul. Unfortunately, delay problems occur when different types of technologies are utilized for the backhaul communication network.
FIG. 1 illustrates telecommunication network 100 in an example of the prior art. Telecommunication network 100 includes MSC 110, base transceiver station (BTS) 120, BTS 125, BTS 130, wireless device 140, and public switched telephone network (PSTN) 150. MSC 110 is coupled BTSs 120 and 125 by T-1 lines 111 and 113 respectively. BTS 130 is coupled to MSC by Ethernet backhaul link 112. Wireless device 140 is in communication with base stations 120, 125, and 130 using a wireless protocol, such as GSM or CDMA. MSC 110 is coupled to PSTN 150 by a trunk connection as is well known in the art. Other elements are possible, such as a base station controller, but are not shown for the sake of clarity.
During a call, wireless device 140 transmits communications simultaneously to BTSs 120, 125, and 130. The communications transmitted from wireless device 140 are transported over both T-1 lines 111 and 113, and Ethernet backhaul link 112. The communications arrive at MSC 110. MSC 110 selects the communications from either of the T-1 lines or the Ethernet backhaul link. MSC 110 then routes the communications to their appropriate destination. Communications that are received into MSC 110 from the destination are routed to T-1 lines 111 and 113 and Ethernet backhaul link 112. All three base stations 120, 125, and 130 then transmit the communications to wireless device 140. Wireless device 140 selects one of the three transmitted signals based upon several factors, such as their respective signal strengths.
As is well known in the art, backhaul connections typically involve some amount of delay. In this example, the delay associated with T-1 lines 111 and 113 are relatively similar. Thus, when MSC 110 switches between line 111 and line 113, the two communication streams from each line are adequately synchronized. Unfortunately, the delay associated with Ethernet backhaul link 112 is often times unpredictable. In addition, the delay associated with Ethernet backhaul link 112 is often times much greater than that of T-1 lines 111 and 113. As a result, packets arriving after the time interval where they can be used are discarded, and the end users experience call degradation when MSC 110 switches between one of the T-1 lines and Ethernet backhaul link 112. For instance, the users hear a gap in their conversations. Even more problematically, the call could be dropped entirely. The increased use of WiMAX technologies will further exacerbate the above problems.